The present invention relates generally to a fuel control solenoid valve used in a fuel injection pump of an internal combustion engine such as a diesel engine, more particularly to such a fuel control solenoid valve for optimally controlling the quantity of fuel injection into cylinders of the engine and the timing of the fuel injection thereinto.
It is known in the art of fuel injection timing control that a fuel injection timing is controlled by closing a high pressure chamber of a fuel injection pump. One example of such a fuel injection timing control system is disclosed in Japanese patent Provisional Publication No. 59-155568, the teachings of which involves controlling the fuel injection timing by closing a solenoid-operated valve after the elapse of either a predetermined time period or cam angle from the generation of the output signal of a reference angle sensor occuring at a given interval within the engine operating cycle, the solenoid-operated valve being provided in a passage establishing the communication between the high pressure chamber and low pressure side of the fuel injection pump. This known system is simple in construction as compared with a conventional method of mechanically controlling the fuel injection timing, and is also suitable for electronic control.
There is a problem which arises with such a high pressure chamber-closed type system, however, in that difficulty has been encountered to maintain the valve-closed state withstanding the pressure of up to 800 kg/cm.sup.2 in a line type pump or the pressure of up to 1500 kg/cm.sup.2 in a unit injector in which a pump and a nozzle are integrally constructed as a one-piece unit, and to readily manufacture a solenoid-operated valve with high reliability which is capable of operating with valve closing responsibility of 1500 Hz at maximum in accordance with speeds of the engine.
One possible solution is to use an externally opening type solenoid-operated valve as disclosed in Japanese patent Provisional Publication No. 55-139965. However, this prior art technique does not produce satisfactory results for meeting requirements in terms of adjustment of the valve lifting amount and the valve closing force and build-in of the valve.